As a method for producing an unsaturated acid and/or an ester thereof, such as methacrylic acid (MAA) and/or methyl methacrylate (MMA), the acetone cyanohydrin method (ACH method), which produces methacrylic acid and/or methyl methacrylate from acetone and prussic acid (hydrogen cyanide), has been industrially widely used. However, prussic acid is highly poisonous, and the use thereof is undesirable.
As methods of using no prussic acid, a method of oxidizing isobutene or tertiary butyl alcohol, a method of subjecting propionic acid or propionic acid ester to reaction with formaldehyde or the like, are known. However, any of them have problems when practiced industrially.
A method for producing methacrylic acid or a methacrylic acid ester from a 1,1,1-trihalo-2-methyl-2-propanol is also known. For instance, there is a known method in which 2-methoxy-2-methylpropanoic acid is obtained from 1,1,1-trichloro-2-methyl-2-propanol, then converted into a methyl ester thereof and further dealcoholized, to thereby produce methyl methacrylate (Non-patent Document 1). In producing 2-methoxy-2-methylpropanoic acid, such a method, however, requires to use a basic compound in an amount three times by mole larger than that of the alcohol as a starting material. In addition, in producing methyl methacrylate from methyl 2-methoxy-2-methylpropanoate, one or more equivalent of phosphorous compound or metal chloride is required. Consequently, this method cannot be said to be industrially practicable production method. Further, the chlorine component in the starting material combines with the basic compound to form a salt, and which is difficult to use effectively so long as it remains in a salt form.
As another method for producing methacrylic acid, a method in which 2-chloro-2-methylpropanoic acid is heated up to a temperature of 250° C. to 600° C. in the presence of a catalyst such as calcium chloride is known (Patent Document 1). Further, as a method for producing methyl methacrylate, a method in which methyl 2-chloro-2-methylpropanoate is used as a starting material, heated up to a temperature of 480° C. to 550° C. without catalyst, and then heated up to a temperature of 250° C. to 350° C. in the presence of a dehydrohalogenation catalyst such as a metal chloride is known (Patent Document 2). The 2-chloro-2-methylpropanoic acid and the methyl 2-chloro-2-methylpropanoate can be produced according to, for example, the method for producing 2-bromo-2-methylpropanoic acid through the reaction between 1,1,1-tribromo-2-methyl-2-propanol and potassium hydroxide (Non-patent Document 2). In each of these methods, however, it is required to use the basic compound in an amount two times by mole larger than that of the alcohol as a starting material. Further, the obtained halogen salt is difficult to be used effectively.